The present invention relates to an idle stop control device for a vehicle, such as an automobile, especially for the vehicle provided with an automatic transmission, and belongs to a field of traveling control technique of the vehicle.
In recent years, vehicles which perform what is called “idle stop control”, where an engine is automatically stopped when a predetermined stop condition is satisfied and the engine is automatically restarted when a predetermined restart condition is satisfied upon the vehicle stopping at an intersection or the like, are put in practical use.
When carrying out the idle stop control in a vehicle equipped with an automatic transmission, an oil pump which is driven by the engine to supply an operating pressure to each friction element of the automatic transmission is also stopped at the time of the engine stop. Therefore, a friction element which is coupled just before the vehicle stop (in other words, a friction element which transmits a motive force at the time of a vehicle start) is once released and, then, it will be again coupled at the time of an engine restart. However, in such a case, problems such as degradation of a vehicle starting performance due to a response delay of the coupling and a shock associated with the coupling occur.
JP2003-39988A discloses an engine automatic stop/start device which is provided with an electric oil pump driven by an electric motor, in addition to the oil pump driven by the engine. An operating pressure is applied from the electric oil pump to the friction element to maintain the friction element in a state where it is coupled also during the engine stop. Accordingly, the degradation of the vehicle starting performance due to the response delay of coupling of the friction element at the time of engine restarting and the generation of the shock when coupling the friction element are avoided.
Meanwhile, a vehicle's operator may switch a gear range of the automatic transmission from a traveling range such as D-range to a neutral range such as N-range during or before the automatic stop of the engine when the vehicle is stopped. In this case, since the automatic transmission is controlled so as to evacuate an operating pressure from each friction element, even if the electric oil pump is operated during the engine automatic stop, a friction element which transmits a motive force when the vehicle starts is released. Therefore, when a switching operation is carried out again to the traveling range upon starting of the vehicle, the friction element is again coupled and, due to the coupling delay, the start response after the engine restart is degraded and the shock occurs at the time of coupling the friction element.